1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor memory device. More particularly, the present invention relates to a method of manufacturing a semiconductor memory device having a bottom electrode, which may have a cylindrical-shape, formed in fine cell areas.
2. Description of the Related Art
With a recent trend of more highly-integrated semiconductor memory devices, a design rule of the memory device is reduced, and an area for a unit memory cell thereof is also reduced. A capacitor used in a memory cell of a dynamic random access memory (DRAM) device is required to have a minimum tolerable capacitance sufficient to provide data input/output characteristics and data reading characteristics even though an area thereof is reduced. The reduction of process margins and areas has significantly affected a design of a memory cell capacitor due to the demand as described above. Therefore, various types of a capacitor bottom electrode structure having a three-dimensional structure with a large height have been introduced in order to manufacture a capacitor for maintaining a minimum capacitance even in a reduced space. Among them, a cylindrical-shaped bottom electrode is generally used because it advantageously increases an effective area of a capacitor. Therefore, various technologies regarding a cylindrical-shaped bottom electrode structure and a formation method thereof have been introduced.
Generally, in order to form a cylindrical-shaped bottom electrode, an etch stop layer and a mold oxide layer are formed on a semiconductor substrate having a buried contact formed therein. The mold oxide layer and the etch stop layer are then sequentially dry-etched to form a mold oxide layer pattern and an etch stop layer pattern for defining a node hole exposing the buried contact. A cylindrical-shaped bottom electrode is then formed using the mold oxide layer pattern. After the bottom electrode is formed, the mold oxide layer pattern is removed by a wet etch. In conventional methods of forming a cylindrical-shaped bottom electrode, a silicon nitride layer is generally used as the etch stop layer.
However, in the previously-introduced conventional methods of forming the cylindrical-shaped bottom electrode, an etchant may penetrate through the interface between the bottom electrode and the etch stop layer down to a lower structure, thereby causing damage to the lower structure. In order to prevent this phenomenon, the etch stop layer may be formed thickly to increase a penetration length of the etchant. However, if the thickness of the etch stop layer is increased when the etch stop layer is formed of the silicon nitride layer, the elements in the upper structure may be broken or damaged during dry-etching of the etch stop layer to form the node hole. Further, if the thickness of the etch stop layer is increased, a surface area of the bottom electrode is reduced by as much as the area where the outer wall of the bottom electrode contacts the etch stop layer pattern, thereby failing to provide a desired capacitance.
More specifically, there is a limit in how large the thickness of the etch stop layer may be formed in order to prevent the above problems. Therefore, there is no alternative but to increase a thickness of the mold oxide layer to increase a height of the bottom electrode. However, as the thickness of the mold oxide layer is increased, and a depth of the storage node hole is increased during dry-etching of the storage node hole, a significant deformation of the sectional profile occurs, and a desired sectional profile cannot be maintained, thereby failing to provide a sufficient bottom area of the bottom electrode. The above problems become more serious as the design rule is reduced, which results an increased possibility of generating a twin bit fail in the bottom electrode of a one cylinder stack (OCS) capacitor due to the falling-down of the bottom electrode in addition to failing to provide the desired capacitance.